Torque-limiting clutches

ABSTRACT

A torque-limiting clutch includes an inner member formed with four radial passages each containing a pair of balls. The radially outermost ball of each pair normally seats in a groove in an outer member surrounding the inner member and the radially innermost ball of each pair engages a generally conical surface of the head of a spindle contained in a bore in the inner member and acted on by a spring so as to urge the balls radially outwardly. Under torque overload conditions the balls move radially inwardly to move the spindle against the action of its spring.

United States Patent 1 Eaves et al.

[451 Apr. 17, 1973 [22] Filed:

[ 1 TORQUE-LIMITING CLUTCHES [75] Inventors: Dennis Robert Eaves; HorstBergemann, both of Christchurch, England [73] Assignee: Bishop Eaves &Som Limited, Parkstone, Poole, England Sept. 28, 1971 21 App]. No.:184,410

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS5/1939 Siesel ....64/29 7/1949 Ristow ..64/ 29 1,057,834 5/1959Germany.... ..64/29 884,780 7/1953 Germany .....81/52.4 R

2/ I962 Poland 64/29 Primary Examiner-Allan D. HermannAttorney-Shlesinger, Fitzsirnmons & Shlesinger ABSTRACT Atorque-limiting clutch includes an inner member formed with four radialpassages each containing a pair of balls. The radially outermost ball ofeach pair normally seats in a groove in an outer, member surrounding theinner member and the radially innermost ball of each pair engages agenerally conical surface of the head of a spindle contained in a borein the inner member and acted on by a spring so as to urge the ballsradially outwardly. Under torque overload condi tionsthe balls moveradially inwardly to move the spindle against the action of its spring.

7Clains,5DrawingFigures v so 29 I2 25 1'5 32 ea 7 53 I 55 ZI/ 2 54. 5(020 A TORQUE-LIMITING CLUTCHES BACKGROUND OF THE INVENTION passage, anaxial bore in the outer member containing a spring loaded spindle whichhas a head provided with a generally conical surface which engages theroller means to effect radially outward biasing thereof into engagementwith a seating formation formed in the wall of the bore of the outermember for the transmission of torque between the inner and outermembers, the arrangement being such that, under torque overloadconditions, said roller means is displaced radially inwardly out of saidseating formation and moves the spindle axi ally against the action ofits spring loading.

2. Description of the Prior Art A German Pat. specification No.1.057.834 shows a torque-limiting clutch of the kind referred to whichhas the spindle thereof arranged so that, when it is moved axially onradially inward movement of the roller means, electrical contact meansis operated to terminate the drive transmitted between the inner andouter members. The clutch of German Pat. specification No. 1.057.834 isthus a single-acting torque-limiting clutch in that, as soon as torqueoverload conditions are sensed, the transmission of drive isinterrupted.

If drive were to continue after overload conditions had been reached theouter member would rotate relative to the inner member until onecomplete relative rotation had been effected and then the roller meanswould be urged radially outwardly under the action of the spring loadingacting on the spindle 'to re-engage the roller means in the seatingformation of the outer member.

Continued re-engagement and disengagement of the roller means in itsseating and repeated axial movement of the spindle under and against itsspring loading will result in repeated impacts between the'spindle andthe roller means on the one hand and the roller means and its seatingformation on the other hand resulting in rapid wear of the impactingsurfaces and possible damage thereto.

For a torque-limiting clutch used in a tapping chuck it is importantthat repeated engagement and disengagement of the roller means from itsseating formation should be effected without there being considerablewear or damage of the relatively moving parts of the clutch.

It is accordingly an object of the present invention toprovide atorque-limiting clutch of the kind referred to the design of which issuch as to permit repetitive engagement and disengagement of the rollermeans from the seating formation of the outer member.

SUMMARY OF THE INVENTION The generally conical surface of the head ofthe spindle includes a first portion having a first apical angle and asecond portion having a second apical angle greater than said firstapical angle, the roller means engaging said first portion duringtransmission of torque between the inner and outer members and thespindle moving relative to the inner member into a position in which theroller means engages said second portion when the roller means movesradially inwardly to disengage from the seat formation of the outermember under torque overload conditions.

BRIEF DESCRIPTION OF THE DRAWINGS:

In the drawings FIG. 1 is a longitudinal sectional view of atorquelimiting clutch for use in a tapping chuck and including an innermember, an outer member, balls for the transmission of torque betweenthe inner and outer mem bers and an axially movable spring-loadedspindle for biasing the balls radially outwardly, the parts of theclutch being shown in the relative positions which they occupy duringthe transmission of torque between the inner and outer members,

FIG. 2 is a transverse sectional view of the clutch,

FIG. 3 is a longitudinal sectional view of the clutch corresponding toFIG. 1 but showing the various parts thereof in the relative positionswhich they occupy when torque overload conditions arise,

FIG. 4 is a side view of the spindle contained within DESCRIPTION OF APREFERRED EMBODIMENT The particular form of torque-transmitting clutchshown in the drawings takes the form of a tool adaptor for a tappingchuck and the tool adaptor includes an inner member 11 and an outermember 12 which is fixed axially relative to the inner member 1 1 bymeans of a circlet 13 which is received in aligned circumferentialgrooves formed in the inner surface of the outer member 12 and the outersurface of the inner member 11. The inner member 11 has an axial bore'14 therein in which a spindle 15 is received and the spindle 15includes a head portion 16 and a series of Belleville washers 17 actbetween the head portion 16 and a washer 18 to urge the spindle 15 in adirection away from end portion 19 of the inner member 11. The washer 18is held in position by means of an externally threaded member 20 whichengage with a threaded end portion of the bore 14 and which is providedwith a through bore 21 which receives a portion of the stem 22 of thespindle 15.

As shown clearly in FIG. 2 the inner member 11 is formed with fourequi-angularly spaced passages 23 which extend between the bore 14 ofthe inner member and the outer surface thereof and each of thesepassages accommodates a radially inner ball 24 and a radially outer ball25.

As can be seen most clearly from FIG. 4 the head portion 16 of thespindle 15 includes a generally cylindrical portion formed integral witha generally frustoconical portion 26 and the generally frusto-conicalportion 26 includes a first portion 27 having an apex angle of 60 and asecond portion 28 having an apex angle of The balls 24 and 25 arearranged in the passages 23 so that the innermost ball 24 of each pairengages the generally frusto-conical head portion 26 and so that theradially outermost ball 25 of each pair normally projects radiallyoutwardly of its-passage 23. The outer member 12 is formed with fourequi-angularly spaced axially extending grooves 29 in its inner surfaceand the cross-section of each groove 29 is illustrated in FIG. 5. lncross-section each groove 29 includes a first portion which extendsbetween the positions indicated at A and B in FIG. 5 and this firstportion has a radius of curvature substantially equal to the radius of aball 25 so that in the normal position of the balls 24 and 25 theradially outermost ball 25 of each pair engages in a groove 29 with itscenter on the center of curvature of the first portion of thecross-section of the groove 29. The

second portion of the cross-section of the groove 29 extends between thepositions indicated at A and C in FIG. 5 and this second portion of thegroove 29 is of progressively increasing radius of curvature.

The biasing force exerted by the Belleville washers 17 on the spindlecan be adjusted by adjusting the position of the threaded member withinthe bore 14 of the inner member. As the inner balls 24 engage thegenerally frusto-conical portion 26 of the head 16 of the spindle is,the biasing force exerted by the Belleville washers 17 is transmitted tothe balls 24 and 25 so that the balls are urged radially outwardly andthe balls 25 thus serve to transmit torque between the inner member 11and the outer member 12 while they are seated in their respectivegrooves 29 in the outer balls arranged to seat in a. circumferentialgroove 31 formed in the inner member 11' whereby the inner member 11 isheld against axial movement relative to the drive element of the chuck.

' The other end of the inner member 11 is provided with a socket 32inwhich a sleeve 33 is received, the

sleeve 33 being urged. outwardly of the socket 32 by a spring 34,outward movement of the sleeve 33 being limited by engagement of apin 35with the surrounds of an aperture 36 formed in the wall of the sleeve33. The sleeve 33 is provided with three equi-angularly spaced openingsin which balls 37 are received, each ball 37 having a diameter greaterthan the wall thickness of the sleeve 33. The balls 37 are arranged toseat in a circumferential groove in a tap (not shown) to hold the tapwithin the sleeve and, to disengage the tap from the sleeve 33, thesleeve 33 is moved inwardly into the socket 32 against the action of thespring 34 to bring the balls 37 into register with'a circumferentialgroove 38 formed in the wall of thesocket 32 whereby the balls 37 arefree to move radially outwardly to release the grip on the tap.

During a tapping operation the outer member 12 of the clutch rotates inthe direction indicated by the 29 and thus each ball .25 will tend tomove radially inwards. When the torque transmitted between the inner andouter members exceeds a certain value, the biasing force exerted on thespindle 15 by the Belleville washers 17 will be insufficient to preventthe balls 25 from starting to roll out of their respective grooves 29.

The particular shaping of the second portion AC of the cross-section ofeach groove 29 is such that, when the balls 25 start to roll withinthegrooves 29, the radially inwardly directed force transmitted to eachball 25 will increase as the distance by which each ball has rolledincreases. The condition is thus such that, when overload conditionsarise and the balls 25 start to roll within their grooves 29 suchrolling of the balls within the grooves will continue without itfbeingnecessary for there to be a substantial increase in the torque transmitted between the inner and outer members of the clutch. r

When the balls 25 reach positions in which they are clear of the grooves29, the innermost ball 24 of each pair will have moved from a positionin which it engaged the first portion 27 of the generally frusto-conicalportion 26 of the head 16 of the spindle to a position in which saidball 24 engages the second portion 28 of said surface. The axial forcetransmitted to the spindle 15 to move it against the action of theBelleville washers l7 depends on the inclination of the surface engagedby the innermost balls 24. I

.When, therefore, torque overload conditions are obtained as a resultof, for example, the tap reaching the bottom of a blind bore, the balls24 will initially move over the surface portion 27 and then, when theballs 25 disengage from the grooves 29, the balls 24 will move intoengagementwith the surfaceportion 28. The rate of movement of thespindle 15 is dependent on the axial force exerted thereon by the balls24 and thus the acceleration to which the spindle 15 is subject ontorque overload conditions being obtained is decreased when theinnermost balls 24 move from a position in engagement with thefirst-surface portion-27 into engagement with the second surface portion28. The

degree-of compression of the Belleville washers 17. is

thus less than would be the case if the frusto-conical portion 26 of thehead 16 were of uniform apical angle. After the outermost balls 25 havedisengaged from the grooves 29, continued rotation of the outermemberrelative to the inner member 11 will result in the outer member 12moving into aposition spaced from its original position in which theballs 25 are again in register with grooves 29 in the outer member 12.When such 90 of relative rotation has taken place the Bel-v levillewashers 17 will urge the spindle 15 back towards its original position.lnorderto avoid the transmission of impacts between thehead of thespindle and the balls 24, the generally cylindrical portion of the head16 is shaped so as to provide a shoulder 39 whichabuts a shoulder 40provided by an inturned lip in the bore of the inner member 11.

The relative positions of the shoulders 39' and.40 and is spring urgedback to its original position, the transmission of impacts between theradially innermost balls 24 and the generally frusto-conical surface 26are minimized as are impacts between the radially outermost balls 25 ofeach pair and the bases of the grooves 29.

When, therefore, torque overload conditions arise and the balls 24 and25 are subject to repeated radially inward and radially outward movementand the spindle is subject to repeated movement against and under theaction of its spring loading, the conditions are such as to minimizewear of the balls24 and 25 and the parts which they engage.

After the required tapping operations have been effected and it isrequired to remove a driven tap from a bore in a workpiece, the driveelement in association with the outer member 12 of the clutch is drivenin the reverse direction, i.e., in the direction opposite to the arrowin FIG. 5. When the outer member 12 moves in the direction opposite tothe arrow of FIG. 5, the radially outermost balls 25 of each pair areengaged by those surface portions of the grooves 29 between the points Aand B of FIG. 5. As this part 'of the surface of each groove 29 has aradius of curvature substantially equal to the radius of curvature ofthe balls 25, the radially inward component of the force transmittedbetween the outer member 12 and each ball 25 is substantially less thanthe radially inward component of the force transmitted between the outermember 12 and the balls 25 when the outer member 12 is rotating in thedirection indicated by the arrow in FIG. 5. As a result of this thetorque which can be transmitted between the inner and outer members whenremoving a tap from the workpiece is substantially greater than thetorque which can be transmitted between the inner and outer membersduring a tapping operation.

The various parts of the clutch can thus be set up so that slippingbetween the inner and outer members of the clutch will take place duringa tapping operation as a result of quite small overload conditionswithout there being the possibility of clutch slipping during reverserotation of the tap.

As discussed above the axial component of force transmitted by the balls24 and 25 to the spindle 15 to move it against the action of its springloading when the balls 24 and 25 move radially inwardly under torqueoverload conditions depends on the inclination of the surface of thehead engaged by the balls 25.

By arranging therefore for the ball 25 to engage the second portion 28of the generally conical surface of the head of the spindle when theballs move radially inwardly so that the balls 25 are out of engagementwith the grooves 29 of the outer member 12, the axial component of forceacting on the spindle 15 to move it against its spring loading issubstantially reduced as compared with the force which would act on thespindle if the inclination of the whole of the engaged surface of thehead of the spindle corresponded to that of the first portion 27. Thedistance by which the spindle 15 is displaced is thus also reduced andthis in turn reduces the spring force acting to bias the spindle 15 backtowards its original position.

When, therefore, torque overload conditions occur and the outer member12 rotates relative to the inner member 11 until the balls 25 are againin register with the grooves 29 so that the balls 24 and 25 tend to moveradially outwardly whereby the balls 25 enter the grooves 29, the forceacting to urge each ball 25 radially outwardly will be correspondinglyreduced thus reducing the impact between each ball 25 and the associatedgroove 29.

The stop 40 provided in the bore 14 of the inner member 11 is arrangedto engage the shoulder 39 on the spindle when the balls move radiallyoutwardly, such engagement of the shoulder 39 with the stop 40 beingarranged to take place prior to the balls 24 and 25 having completedtheir radially outward movements so as to avoid the transmission ofimpacts between the balls 24 and the spindle 15.

In order to obtain the maximum possible strength for the inner member ofthe clutch it is desired to reduce, so far as possible, thecircumferential extent of the radial passages 23 formed in the innermember 11 and hence it is desired that the roller means in said passages23 should have the smallest possible diameter. Rather, therefore, thanhave a single ball in each of said passages, a pair of balls 24 and 25are contained in each of said passages, the radially outermost ballbeing arranged to engage with a corresponding groove 29 of the outermember and the radially innermost ball 25 being arranged to engage thegenerally conical surface 26 of the head of the spindle.

In the arrangement shown in the drawing the base of the socket 32 whichreceives the body of the tap is formed with a rectangular cross-sectionbore to receive a rectangular cross-section extension of the tap body toobtain a positive drive connection between the inner member 11 and thetap body.

We claim:

1. In a torque-limiting clutch which includes an outer member having abore which receives an inner member having a radial passage therein,roller means contained in said radial passage, an axial bore in theouter member containing a spring-loaded spindle which has a headprovided with a generally conical surface which engages the roller meansto effect radially outward biasing thereof into engagement with theseating formation formed in the wall of the bore of the outer member forthe transmission of torque between the inner and outer members, thearrangement being such that, under torque overload conditions, saidroller means is displaced radially inwardly out of said seatingformation and moves the spindle axially against the action of its springloading, the improvement wherein the generally conical surface of thehead of the spindle includes a first portion having a first apical angleand a second portion having a second apical angle greater than saidfirst apical angle, the roller means engaging said first portion duringtransmission of torque between the inner and outer members and thespindle moving relative to the inner member into a position in which theroller means engages said second portion when the roller means movesradially inwardly to disengage from the seating formation of the outermember under torque overload conditions and said spindle has a shoulderarranged to engage the stop provided in the bore in the inner member tolimit the extent of movement of the spindle under the action of itsspring loading such engagement of the shoulder and the stop beingarranged to take place prior to the roller means having completed itsradially outward movement so as to avoid the transmission of impactsbetween the roller means and the spindle.

2. A torque-limiting clutch according to claim 1 wherein the innermember is provided with a plurality of equi-angularly spaced radiallyextending passages each of which contains a pair of roller elements, theradially outer roller element of each pair being arranged to engage aseating formation of the outer member and the radially inner rollerelement of each pair being arranged to engage the generally conicalsurface of the head of the spindle.

3. A torque-limiting clutch according to claim 1 wherein the springmeans acting on the spindle comprises a plurality of Belleville washerssurrounding a stem of the spindle and wherein the stem of the spindlepasses through an annular member contained within the bore in the innermember and wherein means are provided for adjusting the axial spacingbetween said annular member and the head of the spindle to vary thespring loading acting on the spindle.

4. A torque-limiting clutch according to claim 1 wherein the seatingformation in the outer member is constituted by a groove of asymmetricalcross-section.

' 5. A torque-limiting clutch according to claim 4 wherein the groovecomprises, in cross-section, a first portion having a radius ofcurvature substantially equal to that of the associated roller means anda center of curvature lying on a line interconnecting the base of memberhaving a radial passage therein, roller means contained in said radialpassage, an axial bore in the inner member containing a spring loadedspindle which has a head provided with a generally conical surface whichengages roller means to effect radially outward biassing thereof intoengagement with the seating formation formed in the wall of the bore ofthe outer member for the transmission of torque between the inner andouter members, the arrangement being such that, under torque overloadconditions, said roller means is displaced radially inwardly out of saidseating formation and moves the spindle axially against the action ofits spring loading, the improvement wherein the inner member is formedwith a plurality of equi-angular spaced radial passages each of whichcontains a pair of balls, the radially innermost ball of each pair beingarranged to engage generally conical surface of the head of the spindleand the outer member of the clutch being formed with a correspondingplurality of seating formations each arranged to receive the radiallyoutermost ball of the associated pair and said spindle has a shoulderarranged to engage a stop provided in the bore of the inner memberto-limit the extent of movement of the spindle under the action of itsspring loading and'wherein means are provided for adjusting said springloading.

7. A torque-limiting clutch according to claim 6 wherein each seatingformation in the outer member is constituted bya groove of asymmetricalcross-section comprising a first portion having a radius of curvaturesubstantially equal to that of a ball and a center of curvature lying ona line interconnecting the base of the groove and the axis of the outermember and a second portion which has a radius of curvature whichincreases progressively from the base ofthe groove to the side thereof.

1. In a torque-limiting clutch which includes an outer member having abore which receives an inner member having a radial passage therein,roller means contained in said radial passage, an axial bore in theouter member containing a spring-loaded spindle which has a headprovided with a generally conical surface which engages the roller meansto effect radially outward biasing thereof into engagement with theseating formation formed in the wall of the bore of the outer member forthe transmission of torque between the inner anD outer members, thearrangement being such that, under torque overload conditions, saidroller means is displaced radially inwardly out of said seatingformation and moves the spindle axially against the action of its springloading, the improvement wherein the generally conical surface of thehead of the spindle includes a first portion having a first apical angleand a second portion having a second apical angle greater than saidfirst apical angle, the roller means engaging said first portion duringtransmission of torque between the inner and outer members and thespindle moving relative to the inner member into a position in which theroller means engages said second portion when the roller means movesradially inwardly to disengage from the seating formation of the outermember under torque overload conditions and said spindle has a shoulderarranged to engage the stop provided in the bore in the inner member tolimit the extent of movement of the spindle under the action of itsspring loading such engagement of the shoulder and the stop beingarranged to take place prior to the roller means having completed itsradially outward movement so as to avoid the transmission of impactsbetween the roller means and the spindle.
 2. A torque-limiting clutchaccording to claim 1 wherein the inner member is provided with aplurality of equi-angularly spaced radially extending passages each ofwhich contains a pair of roller elements, the radially outer rollerelement of each pair being arranged to engage a seating formation of theouter member and the radially inner roller element of each pair beingarranged to engage the generally conical surface of the head of thespindle.
 3. A torque-limiting clutch according to claim 1 wherein thespring means acting on the spindle comprises a plurality of Bellevillewashers surrounding a stem of the spindle and wherein the stem of thespindle passes through an annular member contained within the bore inthe inner member and wherein means are provided for adjusting the axialspacing between said annular member and the head of the spindle to varythe spring loading acting on the spindle.
 4. A torque-limiting clutchaccording to claim 1 wherein the seating formation in the outer memberis constituted by a groove of asymmetrical cross-section.
 5. Atorque-limiting clutch according to claim 4 wherein the groovecomprises, in cross-section, a first portion having a radius ofcurvature substantially equal to that of the associated roller means anda center of curvature lying on a line interconnecting the base of thegroove and the axis of the outer member and a second portion which has aradius of curvature which increases progressively from the base of thegroove to the side thereof, the shaping of said second portion of thegroove serving to facilitate rolling of the associated roller elementout of the groove under torque overload conditions.
 6. In atorque-limiting clutch which includes an outer member which has a borewhich receives an inner member having a radial passage therein, rollermeans contained in said radial passage, an axial bore in the innermember containing a spring loaded spindle which has a head provided witha generally conical surface which engages roller means to effectradially outward biassing thereof into engagement with the seatingformation formed in the wall of the bore of the outer member for thetransmission of torque between the inner and outer members, thearrangement being such that, under torque overload conditions, saidroller means is displaced radially inwardly out of said seatingformation and moves the spindle axially against the action of its springloading, the improvement wherein the inner member is formed with aplurality of equi-angular spaced radial passages each of which containsa pair of balls, the radially innermost ball of each pair being arrangedto engage generally conical surface of the head of the spindle and theouter member of the clutch being formed with a corresponding plUralityof seating formations each arranged to receive the radially outermostball of the associated pair and said spindle has a shoulder arranged toengage a stop provided in the bore of the inner member to limit theextent of movement of the spindle under the action of its spring loadingand wherein means are provided for adjusting said spring loading.
 7. Atorque-limiting clutch according to claim 6 wherein each seatingformation in the outer member is constituted by a groove of asymmetricalcross-section comprising a first portion having a radius of curvaturesubstantially equal to that of a ball and a center of curvature lying ona line interconnecting the base of the groove and the axis of the outermember and a second portion which has a radius of curvature whichincreases progressively from the base of the groove to the side thereof.